The present invention relates to the testing of semiconductor product wafers and, in particular, to the contactless measurement of junction leakage on product wafers.
It is often desirable to make PN junction leakage measurements on product wafers that contain the many PN junctions created in the fabrication process. A simple qualitative leakage measurement may be obtained by examining the median leakage behavior of all the junctions on single chip. This can be done by exciting junctions with light and then examining the area weighted average of the photovoltaic decay of the junctions with one large capacitive sensor that is the approximate size of a product chip. Such a simple method works well when one particular type of junction dominates the general area of the chip. However, quite often, there will be competing opposite polarity surface photovoltage signals from other type junctions on the same chip.
U.S. Pat. No. 4,812,756 shows a method for making general leakage measurements on a wafer utilizing corona charge and is incorporated herein by reference.